Light-emitting device, optical device, and information processing apparatus

ABSTRACT

A light-emitting device includes a light diffusing member that diffuses light emitted from a light source so that an object to be measured is irradiated with the light; and a holding unit that is provided on plural wires connected to the light source and holds the light diffusing member.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based on and claims priority under 35 USC 119 fromJapanese Patent Application No. 2019-039587 filed Mar. 5, 2019.

BACKGROUND (i) Technical Field

The present disclosure relates to a light-emitting device, an opticaldevice, and an information processing apparatus.

(ii) Related Art

Japanese Unexamined Patent Application Publication No. 2018-54769describes an imaging device that includes a light source, a lightdiffusing member that has plural lenses disposed adjacent to one anotheron a predetermined plane and diffuses light emitted from the lightsource, and an imaging element that receives light diffused by the lightdiffusing member and then reflected by a subject, wherein the plurallenses are disposed so that a cycle of an interference fringe of thediffused light is three pixels or less.

SUMMARY

In three-dimensional measurement using a Time of Flight (ToF) method,light emitted from a light source is diffused through a light diffusingmember held by a holding unit so that an object to be measured isirradiated with the light, and a three-dimensional shape of the objectto be measured is measured based on the reflected light.

The light source used for three-dimensional measurement using a Time ofFlight (ToF) method needs to radiate light to a wider range than a lightsource for simple distance measurement and therefore needs to be alarge-output light source.

It is desirable that, for example, a light-emitting device using such alarge-output light source efficiently release heat generated by thelight source.

Aspects of non-limiting embodiments of the present disclosure relate toa light-emitting device and the like that have a structure that allowsheat generated by a light source to be easily released as compared witha case where a holding unit that holds a light diffusing member is notprovided on a wire connected to a light source.

Aspects of certain non-limiting embodiments of the present disclosureaddress the above advantages and/or other advantages not describedabove. However, aspects of the non-limiting embodiments are not requiredto address the advantages described above, and aspects of thenon-limiting embodiments of the present disclosure may not addressadvantages described above.

According to an aspect of the present disclosure, there is provided alight-emitting device including a light diffusing member that diffuseslight emitted from a light source so that an object to be measured isirradiated with the light; and a holding unit that is provided on pluralwires connected to the light source and holds the light diffusingmember.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the present disclosure will be described indetail based on the following figures, wherein:

FIG. 1 illustrates an example of an information processing apparatus;

FIG. 2 is a block diagram for explaining a configuration of theinformation processing apparatus;

FIG. 3 is a plan view of a light source;

FIG. 4 is a view for explaining a cross-section structure of a singleVCSEL in the light source;

FIGS. 5A and 5B are views for explaining an example of a light diffusingmember, FIG. 5A is a plan view, and FIG. 5B is a cross-sectional viewtaken along line VB-VB of FIG. 5A;

FIG. 6 illustrates an example of an equivalent circuit that drives thelight source by low-side driving;

FIGS. 7A and 7B are views for explaining a light-emitting device towhich a first exemplary embodiment is applied, FIG. 7A is a plan view,and FIG. 7B is a cross-sectional view taken along line VIIB-VIIB of FIG.7A;

FIGS. 8A and 8B are views for explaining a light-emitting device forcomparison, FIG. 8A is a plan view, and FIG. 8B is a cross-sectionalview taken along line VIIIB-VIIIB of FIG. 8A;

FIGS. 9A and 9B are views for explaining a light-emitting device towhich a second exemplary embodiment is applied, FIG. 9A is a plan view,and FIG. 9B is a cross-sectional view taken along line IXB-IXB of FIG.9A;

FIGS. 10A and 10B are views for explaining a light-emitting device towhich a third exemplary embodiment is applied, FIG. 10A is a plan view,and FIG. 10B is a cross-sectional view taken along line XB-XB of FIG.10A; and

FIGS. 11A and 11B are views for explaining a light-emitting device towhich a fourth exemplary embodiment is applied, FIG. 11A is a plan view,and FIG. 11B is a cross-sectional view taken along line XIB-XIB of FIG.11A.

DETAILED DESCRIPTION

Exemplary embodiments of the present disclosure are described in detailbelow with reference to the attached drawings.

An information processing apparatus is often configured to determinewhether or not a user who has accessed the information processingapparatus is permitted to access the information processing apparatusand permit the user to use the information processing apparatus only ina case where the information processing apparatus authenticates the useras a user permitted to access the information processing apparatus.Conventionally, a method for authenticating a user by using a password,a fingerprint, an iris, or the like has been used. Recently, there aredemands for an authentication method that provides higher security. Oneexample of such a method is authentication using a three-dimensionalimage such as a shape of a user's face.

The following discusses a mobile information processing terminal as anexample of the information processing apparatus and discusses a casewhere a user is authenticated by recognizing a shape of a face capturedas a three-dimensional image. Note that the information processingapparatus is also applicable to information processing apparatuses, suchas a personal computer (PC), other than a mobile information terminal.

Furthermore, the configurations, functions, methods, and the likedescribed in the exemplary embodiments are also applicable torecognition of a three-dimensional shape other than recognition of ashape of a face, that is, applicable to recognition of a shape of anobject other than a face. Furthermore, a distance to an object to bemeasured may be any distance.

First Exemplary Embodiment Information Processing Apparatus 1

FIG. 1 illustrates an example of an information processing apparatus 1.As described above, the information processing apparatus 1 is, forexample, a mobile information processing terminal.

The information processing apparatus 1 includes a user interface unit(hereinafter referred to as a UI unit) 2 and an optical device 3 thatacquires a three-dimensional image. For example, the UI unit 2 isconfigured such that a display device that displays information for auser and an input device that receives an instruction concerninginformation processing based on a user's operation are unified. Thedisplay device is, for example, a liquid crystal display device or anorganic EL display device, and the input device is, for example, a touchpanel.

The optical device 3 includes a light-emitting device 4 and athree-dimensional sensor (hereinafter referred to as a 3D sensor) 5. Thelight-emitting device 4 radiates light toward an object to be measured(toward a face in this example) in order to acquire a three-dimensionalimage. The 3D sensor 5 acquires light radiated from the light-emittingdevice 4 and then reflected back by a face. In this example, athree-dimensional image of a face is acquired based on a flight time oflight by using a Time of Flight (ToF) method. Hereinafter, a face isreferred to as an object to be measured even in a case where athree-dimensional image of a face is acquired. Note that athree-dimensional image of an object other than a face may be acquired.Acquisition of a three-dimensional image is sometimes referred to as 3Dsensing. The 3D sensor 5 is an example of a light receiving unit.

The information processing apparatus 1 is a computer including a CPU, aROM, and a RAM. Examples of the ROM include a non-volatile rewritablememory such as a flash memory. A program and a constant accumulated inthe ROM are loaded into the RAM and are executed by the CPU, and therebythe information processing apparatus 1 operates to execute various kindsof information processing.

FIG. 2 is a block diagram for explaining a configuration of theinformation processing apparatus 1.

The information processing apparatus 1 includes the optical device 3, anoptical device controller 8, and a system controller 9. The opticaldevice controller 8 controls the optical device 3. The optical devicecontroller 8 includes a shape specifying unit 81. The system controller9 controls the whole information processing apparatus 1 as a system. Thesystem controller 9 includes an authentication processing unit 91.Members such as the UI unit 2, a speaker 92, and a two-dimensionalcamera (referred to as a 2D camera in FIG. 2) 93 are connected to thesystem controller 9.

These constituent elements are described below in order.

The light-emitting device 4 includes a substrate 10, a light source 20,a light diffusing member 30, a driving unit 50, a holding unit 60, andcapacitors 70A and 70B. The light source 20, the driving unit 50, andthe capacitors 70A and 70B are provided on the substrate 10. Thecapacitors 70A and 70B are referred to as capacitors 70 in a case wherethe capacitors 70A and 70B are not distinguished from each other.Although the two capacitors 70A and 70B are illustrated, the number ofcapacitors 70 may be one or may be more than two. Furthermore, passiveelements such as a resistive element 6 and a capacitor 7 are provided onthe substrate 10 so that the driving unit 50 operates. Plural resistiveelements 6 may be provided, and plural capacitors 7 may be provided.

As described later, the light diffusing member 30 is held at apredetermined distance from the substrate 10 by the holding unit 60 soas to cover the light source 20. The state where the light diffusingmember 30 covers the light source 20 refers to a state where the lightdiffusing member 30 is provided on an optical axis of light emitted fromthe light source 20 so that the light emitted from the light source 20passes through the light diffusing member 30. That is, this state refersto a state where the light source 20 and the light diffusing member 30overlap each other in plan view (when viewed in an xy plane illustrated,for example, in FIGS. 3 and 7A, which will be described later) asdescribed later.

The light source 20 of the light-emitting device 4 is a light-emittingelement array including plural light-emitting elements that aretwo-dimensional arranged (see FIG. 3, which will be described later).The light-emitting elements are, for example, vertical cavity surfaceemitting lasers (VCSELs). Hereinafter, it is assumed that thelight-emitting elements are vertical cavity surface emitting lasers(VCSELs). The vertical cavity surface emitting lasers (VCSELs) arereferred to as VCSELs. The light source 20 emits light in a directionperpendicular to the substrate 10. In a case where three-dimensionalsensing is performed by using a ToF method, the light source 20 isrequired to emit, for example, pulsed light of 100 MHz or more whoserise time is 1 ns or less by the driving unit 50. Hereinafter, pulsedlight emitted from the light source 20 is referred to as an emittedlight pulse. For example, in a case of face authentication, a distanceover which light is radiated is approximately 10 cm to approximately 1m. A range of measurement of a 3D shape of an object to be measured isapproximately 1 m square. Accordingly, the light source 20 is alarge-output light source, and therefore it is required that heatgenerated by the light source 20 be efficiently released. The distanceover which light is radiated is referred to as a measurement distance,and the range of measurement of a 3D shape of an object to be measuredis referred to as a measurement range or an irradiation range. A planevirtually provided in the measurement range or the irradiation range isreferred to as an irradiation plane.

Details of the substrate 10, the light source 20, the light diffusingmember 30, the driving unit 50, and the holding unit 60 of thelight-emitting device 4 will be described later.

The 3D sensor 5 includes plural light receiving cells. For example, eachof the light receiving cells is configured to receive pulsed light thatis an emitted light pulse from the light source 20 reflected by anobject to be measured and accumulate an electric charge corresponding toa period it takes for the light to be received. Hereinafter, thereflected pulsed light thus received is referred to as a received pulse.The 3D sensor 5 is a device having a CMOS structure in which each lightreceiving cell includes two gates and electric charge accumulating unitscorresponding to the two gates. By alternately applying a pulse to thetwo gates, a generated photoelectron is transferred to any of the twoelectric charge accumulating units at a high speed. In the two electriccharge accumulating units, an electric charge according to a phasedifference between an emitted light pulse and a received pulse isaccumulated. The 3D sensor 5 outputs, for each light receiving cell as asignal, a digital value according to a phase difference between anemitted light pulse and a received pulse through an AD converter. Thatis, the 3D sensor 5 outputs a signal corresponding to a period fromemission of light from the light source 20 to reception of the light bythe 3D sensor 5. The AD converter may be provided in the 3D sensor 5 ormay be provided outside the 3D sensor 5.

The shape specifying unit 81 of the optical device controller 8 acquiresa digital value obtained for each light receiving cell from the 3Dsensor 5 and calculates a distance to the object to be measured for eachlight receiving cell. Then, the shape specifying unit 81 specifies a 3Dshape of the object to be measured based on the calculated distance.

The authentication processing unit 91 of the system controller 9performs authentication processing concerning use of the informationprocessing apparatus 1 in a case where a 3D shape of an object to bemeasured specified by the shape specifying unit 81 is a 3D shapeaccumulated in advance, for example, in the ROM. Note that theauthentication processing concerning use of the information processingapparatus 1 is, for example, processing for determining whether or notto permit use of the information processing apparatus 1. For example, ina case where it is determined that a 3D shape of a face that is anobject to be measured matches a face shape stored in a storage membersuch as the ROM, use of the information processing apparatus 1 includingvarious applications offered by the information processing apparatus 1is permitted.

The shape specifying unit 81 and the authentication processing unit 91are, for example, realized by a program. Alternatively, the shapespecifying unit 81 and the authentication processing unit 91 may berealized by an integrated circuit such as an ASIC or an FPGA.Alternatively, the shape specifying unit 81 and the authenticationprocessing unit 91 may be realized by software such as a program and anintegrated circuit such as an ASIC.

Although the optical device 3, the optical device controller 8, and thesystem controller 9 are separately illustrated in FIG. 2, the systemcontroller 9 may include the optical device controller 8. Alternatively,the optical device controller 8 may be included in the optical device 3.Alternatively, the optical device 3, the optical device controller 8,and the system controller 9 may be integral with each other.

Next, the light source 20, the light diffusing member 30, the drivingunit 50, and the capacitors 70 that constitute the light-emitting device4 are described before description of the light-emitting device 4.

Configuration of Light Source 20

FIG. 3 is a plan view of the light source 20. The light source 20includes plural VCSELs that are arranged in a two-dimensional array. Itis assumed that the rightward direction and the upward direction of thepaper on which FIG. 3 is drawn are an x direction and a y direction,respectively. A direction orthogonal to the x direction and the ydirection in anticlockwise direction is a z direction. The z, y, and zdirections are common to all of the drawings.

Each of the VCSELs is a light-emitting element configured such that anactive region that serves as a light-emitting region is provided betweena lower multilayer film reflector and an upper multilayer film reflectorstacked on the semiconductor substrate 200 (see FIG. 4, which will bedescribed later) and emits laser light in a direction perpendicular tothe semiconductor substrate 200. It is therefore easy to arrange theVCSELs in a two-dimensional array. The number of VCSELs included in thelight source 20 is, for example, 100 to 1000. The plural VCSELs areconnected in parallel and are driven in parallel. The number of VCSELsdescribed above is an example and need just be set in accordance withthe measurement distance and the measurement range.

An anode electrode 218 (see FIG. 4, which will be described later)common to the plural VCSELs is provided on a surface of the light source20. The anode electrode 218 is connected to anode wires 11A and 11B (seeFIG. 7, which will be described later) provided on the substrate 10through a bonding wire as described later. A cathode electrode 214 isprovided on a rear surface of the light source 20 (see FIG. 4, whichwill be described later). The cathode electrode 214 is joined to a partwith which the cathode electrode 214 makes contact and that is a part ofa cathode wire 12 (see FIG. 7, which will be described later) providedon the substrate 10 with use of an electrically-conductive adhesive. Theelectrically-conductive adhesive is, for example, silver paste. Theanode wires 11A and 11B are sometimes referred to as anode wires, andthe cathode wire 12 is sometimes referred to as a cathode wire.Furthermore, these wires are sometimes referred to as wires connected tothe light source 20. The same applies to other cases.

In this example, it is assumed that a planar shape of the light source20 that is a shape viewed in plan view is a quadrangle. A side surfaceon a +y direction side is referred to as a side surface 21A, a sidesurface on a −y direction side is referred to as a side surface 21B, aside surface on a −x direction side is referred to as a side surface22A, and a side surface on a +x direction side is referred to as a sidesurface 22B. The side surface 21A and the side surface 21B face eachother. The side surface 22A and the side surface 22B connect the sidesurface 21A and the side surface 21B and face each other. The sidesurface 21A is an example of a first side surface, the side surface 21Bis an example of a second side surface, the side surface 22A is anexample of a third side surface, and the side surface 22B is an exampleof a fourth side surface. Structure of VCSEL

FIG. 4 is a view for explaining a cross-section structure of a singleVCSEL in the light source 20. The VCSEL is a VCSEL having a λ resonatorstructure. The upward direction of the paper on which FIG. 4 is drawn isthe z direction.

The VCSEL is configured such that an n-type lower distributed braggreflector (DBR) 202 in which AlGaAs layers having different Alcompositions are alternately stacked, an active region 206 including aquantum well layer sandwiched between an upper spacer layer and a lowerspacer layer, and a p-type upper distributed bragg reflector 208 inwhich AlGaAs layers having different Al compositions are alternatelystacked are stacked in order on the semiconductor substrate 200 such asn-type GaAs. Hereinafter, a distributed bragg reflector is referred toas a DBR.

The n-type lower DBR 202 is a multilayer body including pairs of anAl_(0.9)Ga_(0.1)As layer and an GaAs layer, each of the layers has athickness of λ/4n_(r) (λ is an oscillation wavelength, and n_(r) is arefractive index of a medium), and 40 pairs of these layers are stackedso that these layers are alternately provided. A carrier concentrationafter doping of silicon, which is an n-type impurity, is, for example,3×10¹⁸ cm⁻³.

The active region 206 is configured such that the lower spacer layer,the quantum well active layer, and the upper spacer layer are stacked.For example, the lower spacer layer is an undoped Al_(0.6)Ga_(0.4)Aslayer, the quantum well active layer is an undoped InGaAs quantum welllayer and an undoped GaAs barrier layer, and the upper spacer layer isan undoped Al_(0.6)Ga_(0.4)As layer.

The p-type upper DBR 208 is a multilayer body including pairs of ap-type Al_(0.9)Ga_(0.4)As layer and a GaAs layer, each of the layers hasa thickness of 2/4n_(r), and 29 pairs of these layers are stacked sothat these layers are alternately provided. A carrier concentrationafter doping of carbon, which is a p-type impurity, is, for example,3×10¹⁸ cm⁻³. Desirably, a contact layer made of p-type GaAs is formed ina topmost layer of the upper DBR 208, and a p-type AlAs currentconfinement layer 210 is formed in a lowermost layer of the upper DBR208 or in an inner part of the upper DBR 208.

By etching a semiconductor layer stacked from the upper DBR 208 to thelower DBR 202, a cylindrical mesa (a columnar structure) M is formed onthe semiconductor substrate 200. This causes the current confinementlayer 210 to be exposed on a side surface of the mesa M. An oxidizedregion 210A oxidized from the side surface of the mesa M and anelectrically-conductive region 210B surrounded by the oxidized region210A are formed in the current confinement layer 210 by an oxidationprocess. In the oxidation process, an oxidation speed of the AlAs layeris higher than an oxidation speed of the AlGaAs layer, and the oxidizedregion 210A is oxidized from the side surface of the mesa M toward aninside of the mesa M at an almost constant speed, and therefore a planarshape of the electrically-conductive region 210B becomes a shapereflecting an external shape of the mesa M, i.e., a circular shape, anda center of the shape almost matches an axial direction (the line withalternate long and short dashes) of the mesa M. In the present exemplaryembodiment, the mesa M has a columnar structure.

An annular p-side electrode 212 made of a metal in which Ti/Au and thelike are stacked is formed in a topmost layer of the mesa M. The p-sideelectrode 212 makes ohmic-contact with the contact layer provided in theupper DBR 208. An inner side of the annular p-side electrode 212 servesas a light outlet 212A through which laser light is emitted to anoutside. That is, the VCSEL emits light in a direction perpendicular tothe semiconductor substrate 200, and the axial direction of the mesa Mis an optical axis. Furthermore, the cathode electrode 214 is formed asan n-side electrode on the rear surface of the semiconductor substrate200. Note that a front surface of the upper DBR 208 on an inner side ofthe p-side electrode 212 is a light emission surface.

An insulating layer 216 is provided so as to cover the front surface ofthe mesa M excluding a part of the p-side electrode 212 to which ananode electrode (the anode electrode 218, which will be described later)is connected and the light outlet 212A. The anode electrode 218 isprovided so as to make ohmic-contact with the p-side electrode 212excluding the light outlet 212A. The anode electrode 218 is providedcommon to the plural VCSELs. That is, the p-side electrodes 212 of theplural VCSELs that constitute the light source 20 are connected inparallel by the anode electrode 218.

The VCSEL may oscillate in a single transverse mode or may oscillate ina multiple transverse mode (multi mode). Light output of a single VCSELis, for example, 4 mW to 8 mW. Accordingly, for example, in a case wherethe light source 20 is constituted by 500 VCSELs, light output of thelight source 20 is 2 W to 4 W. Heat generated by such a large-outputlight source 20 is large.

Configuration of Light Diffusing Member 30

FIGS. 5A and 5B are views for explaining an example of the lightdiffusing member 30. FIG. 5A is a plan view, and FIG. 5B is across-sectional view taken along line VB-VB of FIG. 5A. In FIG. 5A, itis assumed that the rightward direction and the upward direction of thepaper on which FIG. 5A is drawn are the x direction and the y direction,respectively. It is assumed that a direction orthogonal to the xdirection and the y direction in anticlockwise direction is the zdirection. Accordingly, in FIG. 5B, the rightward direction and theupward direction of the paper on which FIG. 5B is drawn are the xdirection and the z direction, respectively.

As illustrated in FIG. 5B, the light diffusing member 30 includes aresin layer 32 having irregularities for diffusing light on one surface(in this example, a rear surface on a −z direction side) of a glasssubstrate 31 whose both surfaces are parallel and flat. The lightdiffusing member 30 further widens a divergence angle of light incidentfrom the VCSELs of the light source 20. That is, the irregularities ofthe resin layer 32 of the light diffusing member 30 refract and scatterlight so that a divergence angle β of output light becomes larger than adivergence angle α of the incident light. That is, as illustrated inFIG. 5B, the divergence angle β of the light that has passed through thelight diffusing member 30 and has been output from the light diffusingmember 30 becomes larger than the divergence angle α of the lightemitted from the VCSEL (α<β). This means that use of the light diffusingmember 30 increases an area of an irradiation surface irradiated withlight emitted from the light source 20 as compared with a case where thelight diffusing member 30 is not used. Furthermore, a light density onthe irradiation surface decreases. Note that the light density isirradiance per unit area, and the divergence angles α and β are fullwidth at half maximum (FWHM).

The light diffusing member 30 is, for example, configured such that aplanar shape thereof is a quadrangle, a width W_(x) thereof in the xdirection and a vertical width W_(y) thereof in the y direction are 1 mmto 10 mm, and a thickness t_(d) thereof in the z direction is 0.1 mm to1 mm. In a case where the light diffusing member 30 has the size andshape described above, the light diffusing member 30 is suitableespecially for face authentication of a mobile information terminal andmeasurement of a relatively close range up to approximately severalmeters. The planar shape of the light diffusing member 30 may be any ofother shapes such as a polygonal shape or a circular shape.

Driving Unit 50 and Capacitors 70

In a case where the light source 20 is driven at a higher speed, thelight source 20 is desirably driven by low-side driving. The low-sidedriving refers to a configuration in which a driving element such as anMOS transistor is located on a downstream side of a current pathrelative to a target to be driven such as a VCSEL. Conversely, aconfiguration in which a driving element is located on an upstream sideis referred to as high-side driving.

FIG. 6 illustrates an example of an equivalent circuit that drives thelight source 20 by low-side driving. FIG. 6 illustrates VCSELs of thelight source 20, the driving unit 50, the capacitors 70A and 70B, and apower source 82.

The power source 82 is provided in the optical device controller 8illustrated in FIG. 2. The power source 82 generates a direct-currentvoltage whose + side is a power source potential and whose − side is aground potential. The power source potential is supplied to a powersource line 83, and the ground potential is supplied to a ground line84.

The light source 20 is constituted by plural VCSELs that are connectedin parallel as described above. The anode electrode 218 (see FIG. 4) ofthe VCSELs is connected to the power source line 83 through the anodewires 11A and 11B (see FIG. 7, which will be described later) providedon the substrate 10.

The driving unit 50 includes an n-channel MOS transistor 51 and a signalgenerating circuit 52 that turns the MOS transistor 51 on an off. Adrain of the MOS transistor 51 is connected to the cathode electrode 214(see FIG. 4) of the VCSELs through the cathode wire 12 (see FIG. 7,which will be described later) provided on the substrate 10. A source ofthe MOS transistor 51 is connected to the ground line 84. A gate of theMOS transistor 51 is connected to the signal generating circuit 52. Thatis, the VCSELs of the light source 20 and the MOS transistor 51 of thedriving unit 50 are connected in series between the power source line 83and the ground line 84. The signal generating circuit 52 generates an “Hlevel” signal that turns the MOS transistor 51 on and an “L level”signal that turns the MOS transistor 51 off under control of the opticaldevice controller 8.

One terminal of the capacitor 70A and one terminal of the capacitor 70Bare connected to the power source line 83, and the other terminal of thecapacitor 70A and the other terminal of the capacitor 70B are connectedto the ground line 84. That is, the capacitors 70A and 70B are connectedin parallel with the power source 82. Note that the capacitors 70A and70B are, for example, electrolytic capacitors or ceramic capacitors.

Next, a driving method for driving the light source 20 that is low-sidedriving is described.

First, it is assumed that a signal generated by the signal generatingcircuit 52 of the driving unit 50 is an “L level”. In this case, the MOStransistor 51 is in an off state. That is, no electric current flowsbetween the source and the drain of the MOS transistor 51. Accordingly,no electric current flows through the VCSELs that are connected inseries with the MOS transistor 51. The VCSELs do not emit light.

In this state, the capacitors 70A and 70B are charged by the powersource 82. That is, the one terminal of the capacitor 70A and the oneterminal of the capacitor 70B that are connected to the power sourceline 83 become a power source potential, and the other terminal of thecapacitor 70A and the other terminal of the capacitor 70B that areconnected to the ground line 84 become a ground potential. Thecapacitors 70A and 70B accumulates an electric charge determined bycapacitance, a power source voltage (the power source potential—theground potential), and a time.

Next, when the signal generated by the signal generating circuit 52 ofthe driving unit 50 becomes an “H level”, the MOS transistor 51 shiftsfrom an off state to an on state. This causes the electric chargeaccumulated in the capacitors 70A and 70B to flow (be discharged) to theMOS transistor 51 and the VCSELs that are connected in series. As aresult, the VCSELs emit light.

Then, when the signal generated by the signal generating circuit 52 ofthe driving unit 50 becomes an “L level”, the MOS transistor 51 shiftsfrom an on state to an off state. This stops light emission of theVCSELs. This causes the power source 82 to resume accumulation of anelectric charge in the capacitors 70A and 70B.

As described above, when the signal output by the signal generatingcircuit 52 repeatedly switches between the “L level” and the “H level”,the MOS transistor 51 repeatedly turns on and off, andnon-light-emission, which is a state where light emission is beingstopped, and light emission of the VCSELs are repeated. That is, a lightpulse is emitted from the VCSELs. The repeated on and off of the MOStransistor 51 is sometimes referred to as switching.

Although an electric charge (electric current) may be directly suppliedfrom the power source 82 to the VCSELs without providing the capacitors70A and 70B, a rise time of light emission of the VCSELs is shortened ina case where an electric charge is accumulated in the capacitors 70A and70B and the accumulated electric charge is discharged when the MOStransistor 51 shifts from an off state to an on state so that anelectric current is rapidly supplied to the VCSELs.

The substrate 10 is a multilayer (e.g., three-layer) substrate. That is,the substrate 10 includes a first electrically-conductive layer, asecond electrically-conductive layer, and a thirdelectrically-conductive layer from a side on which the members such asthe light source 20 and the driving unit 50 are mounted. An insulatinglayer is provided between the first electrically-conductive layer andthe second electrically-conductive layer and between the secondelectrically-conductive layer and the third electrically-conductivelayer. For example, the third electrically-conductive layer is used asthe power source line 83, and the second electrically-conductive layeris used as the ground line 84. The first electrically-conductive layerforms the anode wires 11A and 11B and the cathode wire 12 (see FIG. 7,which will be described later) of the light source 20 and forms acircuit pattern of a terminal or the like to which the members such asthe capacitors 70A and 70B are connected. The firstelectrically-conductive layer, the second electrically-conductive layer,and the third electrically-conductive layer are made, for example, of anelectrically-conductive material such as electrically-conductive pastecontaining a metal such as copper (C) or silver (Ag) or these metals.The insulating layer is made, for example, of an epoxy resin or ceramic.

The power source line 83 of the third electrically-conductive layer isconnected to the anode wires 11A and 11B (see FIG. 7, which will bedescribed later) provided in the first electrically-conductive layerthrough a via. Similarly, the ground line 84 of the secondelectrically-conductive layer is connected, through a via, to thecathode wire 12 (see FIG. 7, which will be described later) provided inthe first electrically-conductive layer, a terminal to which the sourceof the MOS transistor 51 of the driving unit 50 is connected, and thelike. According to the configuration in which the substrate 10 is amultilayer substrate, the power source line 83 is formed by the thirdelectrically-conductive layer, and the ground line 84 is formed by thesecond electrically-conductive layer as described above, fluctuation ofthe power source potential and the ground potential is easily keptsmall.

Light-Emitting Device 4

Next, the light-emitting device 4 is described in detail.

FIGS. 7A and 7B are views for explaining the light-emitting device 4 towhich the first exemplary embodiment is applied. FIG. 7A is a plan view,and FIG. 7B is a cross-sectional view taken along line VIIB-VIIB of FIG.7A. In FIG. 7A, it is assumed that the rightward direction and theupward direction of the paper on which FIG. 7A is drawn are the xdirection and the y direction, respectively. It is assumed that adirection orthogonal to the x direction and the y direction inanticlockwise direction is the z direction. Accordingly, in FIG. 7B, therightward direction and the upward direction of the paper on which FIG.7B is drawn are the x direction and the z directions, respectively. Thesame applies to similar drawings that will be described later.

On the substrate 10 illustrated in FIG. 7A, the anode wires 11A and 11Band the cathode wire 12 formed by the first electrically-conductivelayer are illustrated. In the cross-sectional view of the substrate 10illustrated in FIG. 7B, the anode wires 11A and 11B and the cathode wire12 formed by the first electrically-conductive layer are illustrated,and description of the second electrically-conductive layer that formsthe ground line 84 and the third electrically-conductive layer thatforms the power source line 83 is omitted. Note that the anode wire 11Ais connected to the power source line 83 formed by the thirdelectrically-conductive layer.

As illustrated in FIG. 7A, the anode wires 11A and 11B are provided soas to face each other in the y direction. The cathode wire 12 isprovided between the anode wires 11A and 11B. The anode wires 11A and11B and the cathode wire 12 are spaced apart from each other by apredetermined interval so as not to be short-circuited. The same appliesto other cases. A part where the anode wires 11A and 11B and the cathodewire 12 are not provided is the insulating layer provided between thefirst electrically-conductive layer and the secondelectrically-conductive layer. The insulating layer has lower thermalconductivity than the electrically-conductive material of which thewires such as the anode wires 11A and 11B and the cathode wire 12 aremade.

The light source 20 is provided on the cathode wire 12. In this example,the cathode electrode 214 of the light source 20 and the cathode wire 12are electrically connected. That is, the cathode electrode 214 of thelight source 20 is fixedly attached to the cathode wire 12 with use ofan electrically-conductive adhesive.

Meanwhile, the anode electrode 218 of the light source 20 and the anodewires 11A and 11B are connected through bonding wires 23A and 23B. Theanode electrode 218 and the anode wire 11A are connected through thebonding wire 23A on the side surface 21A side of the light source 20,and the anode electrode 218 and the anode wire 11B are connected throughthe bonding wire 23B on the side surface 21B side of the light source20.

Heat generated by the light source 20 is easy to transmit to the cathodewire 12 with which the cathode electrode 214 makes direct contact.Furthermore, heat generated by the light source 20 is easy to transmitto the anode wires 11A and 11B connected to the anode electrode 218through the bonding wires 23A and 23B.

As is clear from FIG. 3, the array of the VCSELs is provided at a centerof the light source 20 in plan view. Accordingly, to connect the anodeelectrode 218 and the anode wire 11A or the anode wire 11B, the anodewire 11A or the anode wire 11B is connected to a peripheral part of theanode electrode 218 provided on the front surface of the light source 20through the bonding wire 23A or the bonding wire 23B.

In this example, the anode wires 11A and 11B are provided on the sidesurfaces 21A and 21B of the light source 20 on the ±y direction sidesand are connected to the anode electrode 218 through the bonding wires23A and 23B, respectively. With this configuration, electric currentsare supplied to the light source 20 concurrently from the y directionsides. If a bonding wire is provided on either the +y direction side orthe −y direction side of the anode electrode 218 and an electric currentis supplied to the light source 20, a VCSEL closer to the bonding wirehas a higher current density and a higher intensity of emitted light,and a VCSEL farther from the bonding wire has a lower current densityand a lower light intensity. Hereinafter, the intensity of emitted lightis referred to as a light intensity. That is, imbalance in output lightintensity is more likely to occur among the plural VCSELs of the lightsource 20.

The one terminal of the capacitor 70A is connected to the anode wire 11Athrough a wire (not illustrated). The anode wire 11A is connected to thepower source line 83 formed by the third electrically-conductive layer.Accordingly, the one terminal of the capacitor 70A is connected to thepower source line 83. The other terminal of the capacitor 70A isconnected to the ground line 84 formed by the secondelectrically-conductive layer through a via (not illustrated) (see FIG.6). The one terminal of the capacitor 70B is connected to the anode wire11B through a wire (not illustrated). The anode wire 11B is connected tothe power source line 83 formed by the third electrically-conductivelayer. Accordingly, the one terminal of the capacitor 70B is connectedto the power source line 83. The other terminal of the capacitor 70B isconnected to the ground line 84 formed by the secondelectrically-conductive layer through a via (not illustrated) (see FIG.6).

As described above, since the anode electrode 218 of the light source 20is connected to the different anode wires 11A and 11B through thebonding wires 23A and 23B provided in the ±y directions, the capacitors70A and 70B are provided for the anode wires 11A and 11B, respectively.

In FIG. 7A, the driving unit 50 is connected to the cathode wire 12.This is because the drain of the MOS transistor 51 of the driving unit50 is connected to the cathode of the VCSELs of the light source 20 asillustrated in FIG. 6. The source of the MOS transistor 51 is connectedto the ground line 84 formed by the second electrically-conductive layerthrough a via (not illustrated). Furthermore, the signal generatingcircuit 52 of the driving unit 50 is connected to the power source line83 formed by the third electrically-conductive layer and the ground line84 formed by the second electrically-conductive layer through a via (notillustrated).

On the substrate 10, the members such as the light source 20 and thedriving unit 50 are provided, and the light diffusing member 30 isprovided so as to overlap the light source 20 in plan view with theholding unit 60 interposed therebetween, as illustrated in FIG. 7B. Thelight diffusing member 30 is provided on an optical axis of the lightsource 20. That is, the light diffusing member 30 is provided so as tocover the light source 20 so that the light source 20 and the lightdiffusing member 30 overlap each other in plan view. This causes lightemitted from the light source 20 to pass through the light diffusingmember 30 so that an object to be measured provided in an outside isirradiated with the light.

As illustrated in FIG. 7A, the holding unit 60 is constituted by fourwalls 61A, 61B, 62A, and 62B that are provided so as to surround thelight source 20. The walls 61A and 61B face each other with the lightsource 20 interposed therebetween, and the walls 62A and 62B connect thewalls 61A and 61B and face each other with the light source 20interposed therebetween. That is, the walls 61A, 61B, 62A, and 62Bconstitute sides of a quadrangle in plan view. Lower surfaces (−zdirection side) of the walls 61A, 61B, 62A, and 62B are attached to thesubstrate 10 side, and upper surfaces (+z direction side) of the walls61A, 61B, 62A, and 62B are attached to the light diffusing member 30.That is, four sides of the light diffusing member 30 whose planar shapeis a rectangle are held by the walls 61A, 61B, 62A, and 62B of theholding unit 60. In a case where the walls 61A, 61B, 62A, and 62B arenot distinguished from each other, the walls 61A, 61B, 62A, and 62B aresometimes referred to as walls.

The holding unit 60 is, for example, a member that is integrally moldedfrom a resin material such as liquid crystal polymer or an insulatingmaterial such as ceramic, and a thickness of the walls of the holdingunit 60 is 300 μm, and a height of the walls of the holding unit 60 is450 μm to 550 μm. The holding unit 60 is desirably configured to absorblight emitted from the light source 20. For example, the color of theholding unit 60 is black. This keeps light emitted from the light source20 toward the walls from radiating to an outside without passing throughthe light diffusing member 30.

As illustrated in FIGS. 7A and 7B, the lower surfaces of the walls 61A,61B, and 62B and a part of the wall 62A of the holding unit 60 areprovided on the anode wires 11A and 11B and the cathode wire 12. Thatis, the lower surface of the holding unit 60 is provided on the anodewires 11A and 11B and the cathode wire 12 made of anelectrically-conductive material. This allows heat generated by thelight source 20 to be released from the substrate 10 through the anodewires 11A and 11B and the cathode wire 12 and allows the heat to easilytransmit to the holding unit 60 from the anode wires 11A and 11B and thecathode wire 12 and be released from the light diffusing member 30. Notethat the holding unit 60 is desirably made of a material, such asceramic (e.g., aluminum nitride or silicon nitride), having good thermalconductivity.

The light source 20 and the wires such as the anode wires 11A and 11Band the cathode wire 12 may be directly provided on the substrate 10.Alternatively, the light source 20 and the wires such as the anode wires11A and 11B and the cathode wire 12 may be directly provided on a basemember such as a base member for heat release made of a material, suchas ceramic (e.g., aluminum nitride or silicon nitride), having goodthermal conductivity, and this base member may be provided on thesubstrate 10.

Light-Emitting Device 4′ for Comparison

FIGS. 8A and 8B are views for explaining a light-emitting device 4′ forcomparison. FIG. 8A is a plan view, and FIG. 8B is a cross-sectionalview taken along line VIIIB-VIIIB of FIG. 8A. In the followingdescription, parts identical to the parts of the light-emitting device 4to which the first exemplary embodiment illustrated in FIGS. 7A and 7Bis applied are given identical reference signs, and description thereofis omitted. The following describes differences from the first exemplaryembodiment. The light-emitting device 4′ is referred to as thelight-emitting device 4′ according to a comparative example.

As illustrated in FIG. 8A, the light-emitting device 4′ according to thecomparative example is configured such that anode wires 11A′ and 11B′are provided in parts to which bonding wires 23A and 23B are connected.That is, the lower surfaces of the walls 61A and 61B of the holding unit60 are not provided on the anode wires 11A′ and 11B′. As in thelight-emitting device 4, only a part of the wall 62B of the holding unit60 is provided on the cathode wire 12.

Accordingly, in the light-emitting device 4′, heat generated by thelight source 20 is hard to transmit to the holding unit 60 and bereleased from the light diffusing member 30. That is, in thelight-emitting device 4′, heat from the light source 20 is harder to bereleased than in the light-emitting device 4. It is therefore necessaryto keep electric power supplied to the light source 20 small and keep alight intensity of the light source 20 low in order to keep atemperature of the light source 20 equal to or lower than apredetermined temperature.

In the light-emitting device 4 to which the first exemplary embodimentis applied, the holding unit 60 is provided on the anode wires 11A and11B and the cathode wire 12. With this configuration, the light-emittingdevice 4 is improved in terms of efficiency of heat release from thelight source 20 as compared with the light-emitting device 4′. In thelight-emitting device 4, it is therefore easy to keep the temperature ofthe light source 20 equal to or lower than the predetermined temperatureeven in a case where electric power supplied to the light source 20 isincreased. Consequently, an intensity of light from the light source 20may be increased.

Second Exemplary Embodiment

A light-emitting device 4A to which a second exemplary embodiment isapplied is different from the light-emitting device 4 to which the firstexemplary embodiment is applied in terms of a shape of a cathode wireprovided on a substrate 10 and thereby improves the effect of heatrelease from a light source 20. In the following description, partsidentical to the parts of the light-emitting device 4 to which the firstexemplary embodiment is applied illustrated in FIGS. 7A and 7B are givenidentical reference signs, and description thereof is omitted. Thefollowing describes differences from the first exemplary embodiment.

FIGS. 9A and 9B are views for explaining the light-emitting device 4A towhich the second exemplary embodiment is applied. FIG. 9A is a planview, and FIG. 9B is a cross-sectional view taken along line IXB-IXB ofFIG. 9A.

As illustrated in FIG. 9A, the light-emitting device 4A has a cathodewire 12A, which is obtained by stretching the cathode wire 12 in thelight-emitting device 4 illustrated in FIG. 7A toward the −x directionside. That is, the stretched cathode wire 12A is provided between theanode wires 11A and 11B of the light-emitting device 4. With thisconfiguration, a part of a wall 62A of a holding unit 60, which isprovided on the insulating layer of the substrate 10 in thelight-emitting device 4, is provided on the cathode wire 12A. Asdescribed above, heat generated by the light source 20 is easier totransmit to the cathode wire 12A that is in direct contact with acathode electrode 214 than to anode wires (the anode wires 11A and 11B)from an anode electrode 218 through bonding wires 23A and 233.Accordingly, in the light-emitting device 4A, heat transfers to the wall62A of the holding unit 60 not only from the anode wires 11A and 11B,but also from the cathode wire 12A.

The light-emitting device 4A according to the second exemplaryembodiment has improved heat release efficiency since an area of theholding unit 60 provided on the wires (specifically, the anode wires 11Aand 11B and the cathode wire 12A) in the light-emitting device 4Aaccording to the second exemplary embodiment is larger than an area ofthe holding unit 60 provided on the wires (specifically, the anode wires11A and 11B and the cathode wire 12) in the light-emitting device 4.

Third Exemplary Embodiment

In the light-emitting device 4A to which the second exemplary embodimentis applied, heat release efficiency is improved by changing a shape of acathode wire of the light-emitting device 4 to which the first exemplaryembodiment is applied. In a light-emitting device 4B to which a thirdexemplary embodiment is applied, efficiency of heat release from a lightsource 20 is improved by changing a shape of anode wires. In thefollowing description, parts identical to the parts of thelight-emitting device 4 to which the first exemplary embodiment isapplied illustrated in FIGS. 7A and 7B are given identical referencesigns, and description thereof is omitted. The following describesdifferences from the first exemplary embodiment.

FIGS. 10A and 10B are views for explaining the light-emitting device 4Bto which the third exemplary embodiment is applied. FIG. 10A is a planview, and FIG. 10B is a cross-sectional view taken along line XB-XB ofFIG. 10A.

As illustrated in FIG. 10A, the light-emitting device 4B has an anodewire 11C, which is obtained by connecting the anode wires 11A and 11B ofthe light-emitting device 4 illustrated in FIG. 7A on an outer side of acathode wire 12 on the −x direction side. A whole wall 62A of a holdingunit 60 is provided on the anode wire 11C.

As in the light-emitting device 4A according to the second exemplaryembodiment, the light-emitting device 4B has improved heat releaseefficiency since an area of walls 61A, 61B, 62A, and 62B of the holdingunit 60 provided on the wires (specifically, the anode wire 11C and thecathode wire 12) in the light-emitting device 4B is larger than an areaof the walls 61A, 61B, 62A, and 62B of the holding unit 60 provided onthe wires (specifically, the anode wires 11A and 11B and the cathodewire 12) in the light-emitting device 4.

Fourth Exemplary Embodiment

In the light-emitting device 4B to which the third exemplary embodimentis applied, bonding wires 23A and 23B that connect an anode electrode218 and the anode wire 11C are provided on the ±y direction sides of thelight source 20. Heat transfers from the light source 20 to the anodewire 11C through a bonding wire. It is therefore effective to increasethe number of bonding wires in order to improve efficiency of heatrelease from the light source 20.

FIGS. 11A and 11B are views for explaining the light-emitting device 4Cto which the fourth exemplary embodiment is applied. FIG. 11A is a planview, and FIG. 11B is a cross-sectional view taken along line XIB-XIB ofFIG. 11A.

As illustrated in FIG. 11A, the light-emitting device 4C is configuredsuch that a bonding wire 23C that connects the anode electrode 218 andthe anode wire 11C is provided on the −x direction side of the lightsource 20. This increases an amount of heat transmitted from the lightsource 20 to the anode wire 11C. Furthermore, an electric current issupplied not only from the ±y direction sides but also from the −xdirection. With this configuration, an amount of heat released throughthe anode wire 11C, the holding unit 60, and the light diffusing member30 increases. Furthermore, imbalance in output light intensity is lesslikely to occur among plural VCSELs of the light source 20.

Therefore, the light-emitting device 4C has improved heat releaseefficiency as compared with the light-emitting device 4B to which thethird exemplary embodiment is applied.

Although the light diffusing member 30 is used in the first throughfourth exemplary embodiments, the first through fourth exemplaryembodiments may be applied to a configuration in which a member thattransmits light, for example, a transparent base member such as aprotection covering or an optical member such as a light collecting lensor a micro lens array is used instead of the light diffusing member 30.

Furthermore, a diffractive optical element may be used as the lightdiffusing member 30 in each of the first through fourth exemplaryembodiments. That is, a member that causes incident light to branch bydiffraction is also an example of the light diffusing member 30. In acase where a diffractive optical element is used, the optical device 3may be a light source for a structured light method instead of a devicefor a ToF method.

Electrical insulating coating such as solder resist may be provided onwires such as an anode wire (the anode wire 11A, 11A′, 11B, 11B′, 11C)and a cathode wire (12, 12A) in the first through fourth exemplaryembodiments or no electrical insulating coating such as solder resistmay be provided on wires such as an anode wire (the anode wire 11A,11A′, 11B, 11B′, 11C) and a cathode wire (12, 12A) in the first throughfourth exemplary embodiments. The holding unit 60 may be provided on theelectrical insulating coating such as solder resist or may be providedon an exposed wire that is not coated with coating.

The foregoing description of the exemplary embodiments of the presentdisclosure has been provided for the purposes of illustration anddescription. It is not intended to be exhaustive or to limit thedisclosure to the precise forms disclosed. Obviously, many modificationsand variations will be apparent to practitioners skilled in the art. Theembodiments were chosen and described in order to best explain theprinciples of the disclosure and its practical applications, therebyenabling others skilled in the art to understand the disclosure forvarious embodiments and with the various modifications as are suited tothe particular use contemplated. It is intended that the scope of thedisclosure be defined by the following claims and their equivalents.

What is claimed is:
 1. A light-emitting device comprising: a light diffusing member that diffuses light emitted from a light source so that an object to be measured is irradiated with the light; and a holding unit that is provided on a plurality of wires connected to the light source and holds the light diffusing member.
 2. The light-emitting device according to claim 1, wherein the light source has an anode electrode and a cathode electrode; and the plurality of wires include at least one of an anode wire connected to the anode electrode and a cathode wire connected to the cathode electrode.
 3. The light-emitting device according to claim 1, wherein the light source has an anode electrode and a cathode electrode; and the plurality of wires include an anode wire connected to the anode electrode and a cathode wire connected to the cathode electrode.
 4. The light-emitting device according to claim 2, wherein the light source is a light-emitting element array having a first side surface and a second side surface that face each other and a third side surface and a fourth side surface that connect the first side surface and the second side surface and face each other; and the holding unit is provided on the anode wire provided on a substrate on both of a first side surface side and a second side surface side.
 5. The light-emitting device according to claim 3, wherein the light source is a light-emitting element array having a first side surface and a second side surface that face each other and a third side surface and a fourth side surface that connect the first side surface and the second side surface and face each other; and the holding unit is provided on the anode wire provided on a substrate on both of a first side surface side and a second side surface side.
 6. The light-emitting device according to claim 4, wherein the holding unit is provided on the anode wire provided on the substrate on a third side surface side.
 7. The light-emitting device according to claim 5, wherein the holding unit is provided on the anode wire provided on the substrate on a third side surface side.
 8. The light-emitting device according to claim 4, wherein the holding unit is provided on the cathode wire provided on the substrate on a third side surface side.
 9. The light-emitting device according to claim 5, wherein the holding unit is provided on the cathode wire provided on the substrate on a third side surface side.
 10. The light-emitting device according to claim 4, wherein the holding unit is provided on the cathode wire provided on the substrate on a fourth side surface side.
 11. The light-emitting device according to claim 5, wherein the holding unit is provided on the cathode wire provided on the substrate on a fourth side surface side.
 12. The light-emitting device according to claim 6, wherein the holding unit is provided on the cathode wire provided on the substrate on a fourth side surface side.
 13. The light-emitting device according to claim 7, wherein the holding unit is provided on the cathode wire provided on the substrate on a fourth side surface side.
 14. The light-emitting device according to claim 8, wherein the holding unit is provided on the cathode wire provided on the substrate on a fourth side surface side.
 15. The light-emitting device according to claim 9, wherein the holding unit is provided on the cathode wire provided on the substrate on a fourth side surface side.
 16. The light-emitting device according to claim 1, wherein the holding unit is made of ceramic.
 17. The light-emitting device according to claim 2, wherein the holding unit is made of ceramic.
 18. An optical device comprising: the light-emitting device according to claim 1; and a light receiving unit that receives light emitted from the light source of the light-emitting device and reflected by the object to be measured, wherein the light receiving unit outputs a signal corresponding to a period from the emission of the light from the light source to the reception of the light by the light receiving unit.
 19. An information processing apparatus comprising: the optical device according to claim 18; and a shape specifying unit that specifies a three-dimensional shape of the object to be measured based on the light emitted from the light source of the optical device, reflected by the object to be measured, and received by the light receiving unit of the optical device.
 20. The information processing apparatus according to claim 19, further comprising an authentication processing unit that performs authentication processing concerning use of the information processing apparatus based on a result of the specifying of the shape specifying unit. 